Summary :
Aim: to report a typical case operated on under endonasal endoscopic surgery. Case report: A 20 year old girl came to the clinic with a left eye exophtalmus. Nasal endoscopy revealed a tumour developped into the left nasal fossa. Imaging allowed to suspect an ethmoidal aneurysmal cyst. CT showed a large tumour involving the left ethmoid, extending into the frontal and maxillary sinuses, with a fluid level in the middle of the tumour. MRI eliminated intracranial extension, showed a cystic component in the middle of the tumour and the presence of hemosiderin signals on T2. Complete resection of the tumour was performed under endoscopic endonasal surgery thanks to a cleavage plane between tumour, periorbit and dura. Follow-up was simple with no recurrence at 2 years. Conclusion: Despite its rarity, this tumour needs to be known by ENT surgeons, and our surgical experience demonstrates that it can be resected endoscopically.